The patch titled
Subject: mm: swap: fix performance regression on sparsetruncate-tiny
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-swap-fix-performance-regression-on-sparsetruncate-tiny.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-fix-performance-regression-on-sparsetruncate-tiny.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Subject: mm: swap: fix performance regression on sparsetruncate-tiny
Date: Thu, 6 Apr 2023 00:18:53 +0800
The ->percpu_pvec_drained was originally introduced by commit d9ed0d08b6c6
("mm: only drain per-cpu pagevecs once per pagevec usage") to drain
per-cpu pagevecs only once per pagevec usage. But after converting the
swap code to be more folio-based, the commit c2bc16817aa0 ("mm/swap: add
folio_batch_move_lru()") breaks this logic, which would cause
->percpu_pvec_drained to be reset to false, that means per-cpu pagevecs
will be drained multiple times per pagevec usage.
In theory, there should be no functional changes when converting code to
be more folio-based. We should call folio_batch_reinit() in
folio_batch_move_lru() instead of folio_batch_init(). And to verify that
we still need ->percpu_pvec_drained, I ran mmtests/sparsetruncate-tiny and
got the following data:
baseline with
baseline/ patch/
Min Time 326.00 ( 0.00%) 328.00 ( -0.61%)
1st-qrtle Time 334.00 ( 0.00%) 336.00 ( -0.60%)
2nd-qrtle Time 338.00 ( 0.00%) 341.00 ( -0.89%)
3rd-qrtle Time 343.00 ( 0.00%) 347.00 ( -1.17%)
Max-1 Time 326.00 ( 0.00%) 328.00 ( -0.61%)
Max-5 Time 327.00 ( 0.00%) 330.00 ( -0.92%)
Max-10 Time 328.00 ( 0.00%) 331.00 ( -0.91%)
Max-90 Time 350.00 ( 0.00%) 357.00 ( -2.00%)
Max-95 Time 395.00 ( 0.00%) 390.00 ( 1.27%)
Max-99 Time 508.00 ( 0.00%) 434.00 ( 14.57%)
Max Time 547.00 ( 0.00%) 476.00 ( 12.98%)
Amean Time 344.61 ( 0.00%) 345.56 * -0.28%*
Stddev Time 30.34 ( 0.00%) 19.51 ( 35.69%)
CoeffVar Time 8.81 ( 0.00%) 5.65 ( 35.87%)
BAmean-99 Time 342.38 ( 0.00%) 344.27 ( -0.55%)
BAmean-95 Time 338.58 ( 0.00%) 341.87 ( -0.97%)
BAmean-90 Time 336.89 ( 0.00%) 340.26 ( -1.00%)
BAmean-75 Time 335.18 ( 0.00%) 338.40 ( -0.96%)
BAmean-50 Time 332.54 ( 0.00%) 335.42 ( -0.87%)
BAmean-25 Time 329.30 ( 0.00%) 332.00 ( -0.82%)
>From the above it can be seen that we get similar data to when
->percpu_pvec_drained was introduced, so we still need it. Let's call
folio_batch_reinit() in folio_batch_move_lru() to restore the original
logic.
Link: https://lkml.kernel.org/r/20230405161854.6931-1-zhengqi.arch@xxxxxxxxxxxxx
Fixes: c2bc16817aa0 ("mm/swap: add folio_batch_move_lru()")
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/swap.c~mm-swap-fix-performance-regression-on-sparsetruncate-tiny
+++ a/mm/swap.c
@@ -222,7 +222,7 @@ static void folio_batch_move_lru(struct
if (lruvec)
unlock_page_lruvec_irqrestore(lruvec, flags);
folios_put(fbatch->folios, folio_batch_count(fbatch));
- folio_batch_init(fbatch);
+ folio_batch_reinit(fbatch);
}
static void folio_batch_add_and_move(struct folio_batch *fbatch,
_
Patches currently in -mm which might be from zhengqi.arch@xxxxxxxxxxxxx are
mm-swap-fix-performance-regression-on-sparsetruncate-tiny.patch
